AB is a vertical pole with B at the ground level and A at the top. A man finds that the angle of elevation of the point A from a certain point C on the ground is $60^\circ$. He moves away from the pole along the line BC to a point D such that CD = 7 m. From D the angle of elevation of the point A is $45^\circ$. Then the height of the pole is

Question

( A ) $\frac{7\sqrt{3}}{2}\frac{1}{\sqrt{3}-1}m$
( B ) $\frac{7\sqrt{3}}{2}\frac{1}{\sqrt{3}+1}m$
( C ) $\frac{7\sqrt{3}}{2}(\sqrt{3}+1)m$
( D ) $\frac{7\sqrt{3}}{2}(\sqrt{3}-1)m$